This invention relates generally to epoxy compositions and, more specifically, to epoxy based adhesive coatings for metallic substrates.
Film adhesive layers are commonly applied to metallic surfaces. Existing film adhesive materials include both composite-bonding and metal-bonding materials. These existing bonding materials do not show adequate adhesive properties, such as peel strength and wedge crack resistance, to make them useable in a production environment for fiber metal laminates. Additionally, film adhesive materials have an inherent thickness that makes film type adhesives less effective when a thin coating is desired. More specifically, film adhesive materials contain a carrier scrim to provide film integrity and bondline thickness control. In many applications, this scrim is not necessary and only adds unnecessary thickness and weight.
In addition to the inherent physical limitation described above, film adhesives are subject to manufacturing limitations. Film adhesives are designed for use in film form only. They are, therefore, unusable as a solution material for continuous processing, such as interposing the adhesive layer with a secondary structure. Additionally, the film adhesive layers do not lend themselves easily to continuous, roll-to-roll manufacturing processes.
Therefore, there is an unmet need in the art for an economical method of durably adhering a very thin adhesive layer to a metal surface.
The present invention provides an epoxy-based adhesive coating for a metallic member. The adhesive coating of the present invention is thinner than the known film adhesive materials and does not include a carrier scrim. As a result, the adhesive coating of the present invention is desirable for applications calling for a thin coating. Further, the adhesive coating of the present invention is usable as a solution material for continuous processing. Therefore, the present invention provides a more economical adhesive than known adhesives.
The epoxy-based adhesive coating includes a first epoxy material including approximately 25% solids by weight and a second curative material including approximately 32% solids by weight. According to one aspect of the present invention, the first epoxy material suitably includes about 3% to about 35% liquid Diglycidylether of Bisphenol-A, about 35% to about 60% solid Diglycidylether of Bisphenol-A, about 10% to about 30% Novolac-Epoxy, and about 5% to about 18% Solid Carboxyxe2x80x94Terminated Acrylonitrilexe2x80x94Butadiene Rubber, and the second curative material suitably includes about 0% to about 100% 4,4xe2x80x2-Diaminodiphenylsulfone, about 0% to about 100% 3,3xe2x80x2-Diaminodiphenylsulfone, and about 0% to about 0.2% Chromium octoate.
Another aspect of the present invention is a method of reinforcing a metallic foil. The method includes preparing a surface of the metallic foil to receive an epoxy based adhesive coating. An epoxy-based adhesive coating is applied and the adhesive coating is a two-part epoxy having a first epoxy material including approximately 25% solids by weight and a second curative material including approximately 32% solids by weight. The epoxy-based adhesive coating is cured on the metallic element.